DOI: 10.1126/science.1146842 , 952 (2007); 318Science

et al.Wu-Lung Chang,Yellowstone Caldera, 2004 to 2006Accelerated Uplift and Magmatic Intrusion of the

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(20, 25). The anglesFe−e = 90° andFe−e = −90°correspond to a kick of the second electron,either to the left or the right. This strong electron-electron Coulomb interaction mediates the doubleionization and creates an entanglement betweenthe two electrons. Electron collisions of this sortin bound systems have been demonstrated di-rectly in pump-probe experiments (26).

This situation is an intramolecular version ofa scattering event downstream of a double slit(27, 6). When either photons (6) or particles(27) are scattered from a beam after passagethrough a double slit, the scattering induces aphase shift, which then leads to a shift of theinterference pattern. If the momentum transfer isnot measured in coincidence (6), the fringe vis-ibility is lost. In this experiment, both electronsare initially delocalized inside the molecule in acompletely coherent single quantum state. Be-fore photoabsorption, both electrons are confinedin the hydrogen ground state, which is symmetricwith respect to its two atomic centers. Thus, weobserved not a scattering between classical lo-calized particles but a coherent entanglement ofthe wave function of the two electrons.

It is instructive to think of the electronic two-body system as split into its subsystems andto consider one subsystem as the environmentof the other. The strong Coulomb interactionentangles the two subsystems and leads to aposition-dependent modification of phase ofthe single-particle wave function inside eachof the two subsystems. The entanglement of theelectrons in the pair is directly visible in theirmutual angular distribution and is furtherevidenced by the observation that selecting themomentum of one electron makes the interfer-ence pattern of its partner reappear. In the spirit

of discussions dating from the early history ofquantum mechanics, one particle can be con-sidered an observer that carries partial informa-tion about the other particle and its path throughthe double slit. The amount of which-way in-formation exchanged between the particles islimited by the observer particle's de Brogliewavelength (28). The key difference betweenthe situation depicted in Fig. 2A (which showsinterference) and Fig. 2B (which shows no in-terference) is that the wavelength of the second,unobserved electron is much shorter in the lattercase.

Our experiment thus reveals that a verysmall number of particles suffices to induce theemergence of classical properties, such as theloss of coherence. A four-body system, such asfragmented molecular hydrogen, acts as a doubleslit in the sense that coherence is lost in a sub-system of entangled electrons. Such a fundamen-tal system facilitates the study of the influenceof interelectronic Coulomb interactions on thecoherence properties of a single electron. In solid-state–based quantum computing devices, suchelectron-electron interaction represents a keychallenge. One advantageous aspect of the finitesystem investigated here is that, theoretically, itis fully tractable at present (29–32).

References and Notes1. C. Jönnson, Z. Phys. A 161, 454 (1961).2. M. Arndt et al., Nature 401, 680 (1999).3. M. Noel, C. Stroud, Phys. Rev. Lett. 75, 1252 (1995).4. E. Joos, H. Zeh, Z. Phys. B 59, 223 (1985).5. W. Zurek, Rev. Mod. Phys. 75, 715 (2003).6. D. A. Kokorowski, A. D. Cronin, T. D. Roberts,

D. E. Pritchard, Phys. Rev. Lett. 86, 2191 (2001).7. L. Hackermüller, K. Hornberger, B. Brezger, A. Zeilinger,

M. Arndt, Nature 427, 711 (2004).

8. H. Cohen, U. Fano, Phys. Rev. 150, 30 (1966).9. D. Rolles et al., Nature 7059, 711 (2005).

10. X. Liu et al., J. Phys. B 39, 4801 (2006).11. I. Kaplan, A. Markin, Sov. Phys. Dokl. 14, 36 (1969).12. M. Walter, J. Briggs, J. Phys. B 32, 2487 (1999).13. J. Fernandez, O. Fojon, A. Palacios, F. Martín,

Phys. Rev. Lett. 98, 043005 (2007).14. N. Stolterfoht et al., Phys. Rev. Lett. 87, 023201 (2001).15. D. Misra et al., Phys. Rev. Lett. 92, 153201 (2004).16. J. Ullrich et al., Rep. Prog. Phys. 66, 1463 (2003).17. R. Dörner et al., Phys. Rep. 330, 95 (2000).18. O. Jagutzki et al., Nucl. Instrum. Methods A 477, 244

(2002).19. T. Weber et al., Nature 431, 437 (2004).20. A. Knapp et al., Phys. Rev. Lett. 89, 033004 (2002).21. G. L. Yudin, S. Chelkowski, A. D. Bandrauk, J. Phys. B 39,

L17 (2006).22. S. K. Semenov, N. A. Cherepkov, J. Phys. B 36, 1409

(2003).23. R. Díez Muiño, D. Rolles, F. J. García de Abajo,

C. S. Fadley, M. A. Van Hove, J. Phys. B 35, L359 (2002).24. T. Opatrny, G. Kurizki, Phys. Rev. Lett. 86, 3180 (2001).25. M. Pont, R. Shakeshaft, Phys. Rev. A 51, R2676 (1995).26. S. N. Pisharody, R. R. Jones, Science 303, 813 (2004).27. K. Hornberger et al., Phys. Rev. Lett. 90, 160401

(2003).28. W. Wootters, W. Zurek, Phys. Rev. D 19, 473 (1979).29. W. Vanroose, F. Martín, T. Rescigno, C. W. McCurdy,

Science 310, 1787 (2005).30. F. Martín et al., Science 315, 629 (2007).31. J. Colgan, M. S. Pindzola, F. Robicheaux, J. Phys. B 37,

L377 (2004).32. D. Dundas, J. Phys. B 37, 2883 (2004).33. We thank M. Walter, J. Briggs, A. Kheifets, U. Becker,

D. Rolles, E. Joos, K. Ueda, M. Arndt, and M. Aspelmeyerfor enlightening discussions. We acknowledgeoutstanding support by the staff of the AdvancedLight Source, in particular by E. Arenholz, T. Young,H. Bluhm, and T. Tyliszczak. This work was supportedby the Deutsche Forschungsgemeinschaft and by theOffice of Basic Energy Sciences, Division of ChemicalSciences of the U. S. Department of Energy undercontract DE-AC03-76SF00098.

10 May 2007; accepted 18 September 200710.1126/science.1144959

Accelerated Uplift and MagmaticIntrusion of the YellowstoneCaldera, 2004 to 2006Wu-Lung Chang,1* Robert B. Smith,1* Charles Wicks,2 Jamie M. Farrell,1 Christine M. Puskas1

The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by GlobalPositioning System and interferometric synthetic aperture radar measurements, at rates up to 7centimeters per year, which is over three times faster than previously observed inflation rates. Sourcemodeling of the deformation data suggests an expanding volcanic sill of ~1200 square kilometers ata 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustalmagma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar tothe amount of magma intrusion required to supply the observed high heat flow of the caldera.This evidence suggests magma recharge as the main mechanism for the accelerated uplift, althoughpressurization of magmatic fluids cannot be ruled out.

TheYellowstone volcanic field is the largestin North America (Fig. 1A). The youngestof three giant eruptions that formed the

field occurred 640,000 years ago, creating the40-km-wide by 60-km-long Yellowstone cal-

dera. This eruption was followed by 30 smallereruptions of dominantly rhyolite flows, theyoungest 70,000 years ago (1). Earthquakes,ground deformation, very high heat flow, andthe world’s largest distribution of hydrothermal

features characterize Yellowstone (2, 3), sim-ilar to those of other silicic volcanic fields suchas Long Valley, California, and Phlegrean Fields,Italy (4, 5).

Geodetic measurements of Yellowstone from1923 to 2004 using precise leveling, GPS (GlobalPositioning System), and InSAR (interfero-metric synthetic aperture radar) have revealedmultiple episodes of caldera uplift and sub-sidence, with maximum average rates of ~1 to2 cm/year generally centered at its two re-surgent domes, Sour Creek and Mallard Lake(6–8). In addition, an area northwest of thecaldera near Norris Geyser Basin experiencedperiods of substantial ground deformation (8, 9).These spatial and temporal variations of the Yel-lowstone unrest also correlated with pronouncedchanges in seismic and hydrothermal activity(9, 10) (Fig. 1B).

1Department of Geology and Geophysics, University ofUtah, Salt Lake City, UT 84112, USA. 2U.S. GeologicalSurvey, MS 977, Menlo Park, CA 94025, USA.

*To whom correspondence should be addressed. E-mail:wchang@earth.utah.edu (W.-L.C.); R.Smith@earth.utah.edu (R.B.S.)

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The University of Utah and the Plate Bound-ary Observatory (PBO) operate twelve continuous-recording GPS stations in Yellowstone to mon-itor ground movement (11) (Fig. 1A). Temporalvariations of the vertical deformation (Fig. 2A)

show 1 to 2 cm of subsidence in the caldera (e.g.,at station LKWY) and uplift in the Norris area(at station NRWY) during the first 6 months of2004. The caldera motion then suddenly re-versed to uplift in July 2004 at unexpected

high rates, ~7 cm/year at station WLWY,whereas the Norris area began to subsideabout 3 months later. Accelerated horizontalmovements correlated in time with the changesin vertical motions (fig. S1). The GPS dataalso reveal a near-simultaneous inception ofuplift across the entire caldera (Fig. 2A), incontrast to the previous observations that de-formation shifted laterally from the SourCreek dome toward the Mallard Lake domein 1 to 2 years (7).

InSAR measurements (ENVISAT IS1 andIS2modes) from 2004 to 2006 (11), with a spatialresolution of ~30 m, reveal ground motions thatare consistent with the GPS observations (Fig.2B and fig. S2). The inflation increases symmet-rically toward the caldera center about the longaxis (northeast-southwest), with the highest rateof ~7 cm/year at the Sour Creek dome beingthree to five times faster than uplift rates in 1923–1984 and 1995–1997 (Fig. 1B). The Norris sub-sidence is ~3 cm/year, more than two timesgreater than the 1996–2002 uplift rate in this area.The GPS horizontal velocities, in addition, indi-cate ground motions directed outward from thecaldera at 0.8 to 2.2 cm/year and inward to theNorris area at 0.7 to 2.0 cm/year.

To evaluate the causes of the observed rapiddeformation, we jointly inverted the GPS andInSAR data (12) for the geometry and expan-sion or contraction of rectangular dislocationsin a homogeneous elastic half-space to sim-ulate inflating and deflating volcanic vol-umes. A nonlinear optimization method wasused to determine the source model that min-imizes the difference between the observedand predicted ground motions (13). Uncer-tainties of model parameters were evaluatedby a c2 method (11).

The best-fitting sources for the GPS andIS2 InSAR data include an expanding sill-like volume dipping 5°SE (5°NW to 15°SE)at a depth of 10 km (6 to 14 km) beneath theYellowstone caldera and a contracting vol-ume dipping 12°SE (7°NW to 18°SE) at a depthof 8 km (6 to 16 km) under the Norris area(Fig. 3). The average rates of volumetric changeare 0.11 km3/year (0.10 to 0.12 km3/year) and–0.01 km3/year (–0.005 to –0.015 km3/year)for the inflating and deflating sources, respec-tively. A joint inversion of the GPS and IS1InSAR data also resulted in similar sourceparameters, indicating the robust nature of themodeling results (fig. S3). Our models, assum-ing uniform constitutive properties, predict ~90%of the observed ground motion within the dataconfidence limits. We also tested the effects ofcrustal heterogeneity by including layers withdifferent elastic constants and showed thatthey would not notably affect our modelingresults (11).

Episodic intrusion or recharge of magmainto the upper crust has been proposed as amechanism for previous Yellowstone calderauplift (1, 2). In this conceptual model, basaltic

Fig. 1. (A) Volcano tectonic setting and GPS station locations of the Yellowstone volcanic field.White circles are earthquake epicenters from October 2004 to March 2007. SC indicates Sour Creekresurgent dome; ML, Mallard Lake resurgent dome; NGB, Norris Geyser Basin; and MHS, MammothHot Springs. GPS station names are abbreviated to four-character codes. Ma, million years ago. (B)Time sequence of Yellowstone vertical ground motions and quarterly earthquake counts. Differentsymbols represent early geodetic measurements (6–9). The yellow shaded area highlights theperiod of accelerated deformation reported in this study. Note that the 1923–1976 and 1976–1984 rates were each determined from only two measurements.

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magma originating from a mantle plume atdepths of ~50 km ascends buoyantly throughthe crust, providing thermal energy to partiallymelt crustal rocks and create the rhyoliticmagma component that characterizes the silicicvolcanism. The basaltic and rhyolitic magmasthen crystallize and cool, releasing energy re-sponsible for Yellowstone’s extraordinarilyhigh heat flow of ~2000 mW/m2 measuredfrom Yellowstone Lake (14) and geochemicalevidence (3).

Seismic tomographic imaging provideddirect evidence for the partially molten crustalmagma chamber beneath the caldera (15).Anomalies of low P-wave velocity, up to 6%,at depths of 8 to 16 km were interpreted as abody of crystallized magma of ~ 4000 km3

directly underlying the caldera. The top of thisbody and our modeled sill overlap (Fig. 3E),implying that the accelerated uplift is causedby inflation from the shallow part of themagma chamber. Moreover, to maintain theobserved caldera heat flux requires a magmacrystallization rate of ~0.1 km3/year (3),

which is comparable to our modeled sourceexpansion rate.

We thus suggest that the 2004–2006 episodeof accelerated inflation occurred in response to acaldera-wide magma recharge of the Yellowstonevolcanic system. Such a high rate of intrusionmayhave occurred during past uplift episodes, forexample between the first two leveling surveys in1923 and 1976, when the caldera rose a total of~75 cm but the rate of 1.4 cm/year was linearlyinterpolated between observations (Fig. 1B).

An alternate interpretation for the calderauplift is that magmatic fluids (water and gases)exsolved frommagma crystallizationwere trappedbeneath impermeable rocks, causing pressuriza-tion of the deep hydrothermal system and in turninflating the ground surface (Fig. 4). Crystallizing0.1 km3/year of rhyolitic magma, which is re-quired to provide the observed thermal heat flow,and trapping all the releasedwater would result ina volumetric expansion of ~0.013 km3/year (3, 16).This value, however, is about 10 times smaller thanthe source inflation rate of 0.11 km3/year respon-sible for the current uplift. Although the volumetric

expansion could be greater if gas discharge istaken into account, this mechanism requires arapid increase in fluid exsolution from magmacrystallization to account for the accelerated cal-dera uplift and is thus a less viable cause for theobserved deformation.

Source modeling of early episodes of calderainflation (7, 17) imply geometries and depthssimilar to those from our model but much lowerrates of volumetric increase, 0.01 to 0.03 km3/year,which are comparable to the rates from the abovemagmatic fluid model. This evidence suggeststhat pressurizing fluid systems near the top of thecrustal magma reservoir is a plausible sourcemechanism for the previous uplift episodes.Therefore, magma intrusion and fluid pressuriza-tion should be considered as jointly operatingprocesses to explain the accelerated caldera upliftreported here, although our estimate of largevolume increase implies the former as a preferredsource model. Further independent observations,such as temporal microgravity changes, capable ofresolving mass and density variations of themagmatic reservoir would be useful to discrim-

Fig. 2. (A) Temporal variation of vertical ground motions of labeledYellowstone GPS stations. Each dot represents a daily position determination.Light gray bars are 1-s errors. Red and blue dot-dash lines mark the inceptionsof the uplift and the subsidence, respectively. Deformation rates are the slopesof the interpolated lines. (B) A stacked InSAR interferogram (ENVISAT IS2 mode)from 22 September 2004 to 23 August 2006 overlain with averaged GPS

velocities from 07 October 2004 and 07 October 2006. The line-of-sight (LOS)displacement of Earth’s surface toward the satellite from the interferograminfers a total uplift of about 11 cm in the west part of the caldera and as large as15 cm at the Sour Creek resurgent dome and a subsidence of 6.6 cm near theNorris Geyser Basin. White and black arrows represent horizontal and verticalvelocity vectors, respectively. Black ellipses and bars are scaled 2-s errors (11).

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inate the contribution between the two differentvolcanic mechanisms (18, 19).

The inflation of the magmatic sill can in-duce dilatational strain in the surroundingvolcanic rocks (Fig. 4), leading to an increasein permeability and a decrease in pore pressureby opening new or self-sealed fractures. Accord-ingly, the dilated zone beneath the northerncaldera can experience lower pore pressurerelative to the hydrothermal reservoirs beneaththe Norris area. This induced pressure gradientcan thereby drive fluids southeastward intothe caldera, depressurizing the Norris hydro-thermal systems and causing the ground thereto subside. Previous studies also implied thatthe widespread hydrothermal and volcanicfeatures across the northern caldera boundaryindicate highly fractured and permeable crustalrocks, providing pathways for fluid migration(9, 16).

We therefore propose that the 2004–2006deflation near Norris Geyser Basin was in re-sponse to a redistribution of hydrothermal fluidsas a consequence of caldera inflation. Moreover,earthquake activity during the deformation peri-

od was concentrated near the northern calderaboundary, while the rest of the caldera experi-enced low rates of seismicity (Fig. 1A). Volu-metric expansion of crustal rocks due to theinduced dilatation can increase the strain rate andpromote brittle fracturing. With fluids migratingfrom the Norris region into the caldera, earth-quakes can be induced within the dilated zonebetween the inflating and deflating source vol-umes (Fig. 4).

The caldera-wide accelerated uplift reportedhere is interpreted as magmatic recharge of theYellowstone magma body (20). Although thegeodetic observations and models do not implyan impending volcanic eruption or hydrothermalexplosion, they are important evidence of on-going processes of a large caldera that wasproduced by a super volcano eruption.

References and Notes1. R. L. Christiansen, U.S. Geol. Surv. Prof. Pap. 729-G

(2001).2. R. B. Smith, L. W. Braile, J. Volcanol. Geotherm. Res. 61,

121 (1994).3. R. O. Fournier, Annu. Rev. Earth Planet. Sci. 17, 13

(1989).

4. D. P. Hill, Geol. Soc. London Spec. Publ. 269, 1(2006).

5. G. De Natale et al., Geol. Soc. London Spec. Publ. 269,25 (2006).

6. D. Dzurisin, K. M. Yamashita, J. W. Kleinman, Bull. Volcanol.56, 261 (1994).

7. C. Wicks, W. Thatcher, D. Dzurisin, Science 282, 458(1998).

8. C. M. Puskas, R. B. Smith, C. M. Meertens, W. L. Chang,J. Geophys. Res. 112, 10.1029/2006JB004325 (2007).

9. C. Wicks, W. Thatcher, D. Dzurisin, J. Svarc, Nature 440,72 (2006).

10. G. P. Waite, R. B. Smith, J. Geophys. Res. 107, 10.1029/2001JB000586 (2002).

11. Materials and methods are available as supportingmaterial on Science Online.

12. After several tests we chose to weigh the GPS velocitymeasurements by a factor of 5 to equal the contributionof the GPS and InSAR data sets to the inversion.

13. P. Cervelli et al., J. Geophys. Res. 107, 10.1029/2001JB000602 (2002).

14. P. Morgan, D. D. Blackwell, R. E. Spafford, R. B. Smith,J. Geophys. Res. 82, 3719 (1977).

15. S. Husen, R. B. Smith, G. P. Waite, J. Volcanol. Geotherm.Res. 131, 397 (2004).

16. D. Dzurisin, J. C. Savage, R. O. Fournier, Bull. Volcanol.52, 247 (1990).

17. D. W. Vasco, C. M. Puskas, R. B. Smith, C. M. Meertens,J. Geophys. Res. 112, 10.1029/2006JB004641 (2007).

18. M. Battaglia, C. Roberts, P. Segall, Science 285, 2119(1999).

Fig. 3. (A) Observed Yellowstone ground motion, 2004–2006. Black andwhite arrows are vertical and horizontal velocity vectors, respectively, measuredby GPS. Background colors represent average LOS velocities interpolated byreduced InSAR data points (gray crosses) (11). (B) Modeled ground motion.Surface projections of the modeled expanding and contracting sills are shownby red and gray rectangles, respectively. Solid lines highlight the tops of thesills. (C) Modeled and observed ground motion along the profile A-A’ in (B). (D)

Residuals between data and model predictions. (E) Three-dimensional view(from the southwest) of the modeled volcanic sills superimposed on aseismically imaged magma body (15). (F) Opening distribution of the modeledinflating sill. We first assumed a uniform dislocation beneath the caldera tosolve for the geometry of the sill. The dislocation was then discretized into 30patches, and the opening of each was estimated to best explain the spatialvariation of the caldera uplift (11).

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19. J. Gottsmann, A. Folch, H. Rymer, J. Geophys. Res. 111,10.1029/2005JB003745 (2006).

20. Updated GPS data show that this episode of Yellowstonecaldera uplift is continuing as of September 2007 (fig. S1).

21. R. B. Smith, R. L. Bruhn, J. Geophys. Res. 89, 5733 (1984).22. S. Husen, R. B. Smith, Bull. Seismol. Soc. Am. 94, 880

(2004).23. This project has been a cooperative effort of the

University of Utah, the Yellowstone Volcano Observatory,

and the EarthScope PBO. ENVISAT data were providedby the European Space Agency as part of Cat-1project 2765. Discussions with R. Fournier, C. Meertens,G. Waite, H. Heasler, and J. Lowenstern greatlybenefited the paper. M. Poland, S.-H. Yun, and threeanonymous reviewers provided constructive comments.The research was funded by the NSF ContinentalDynamics Program, grant no. EAR0314237, and TheBrinson Foundation.

Supporting Online Materialwww.sciencemag.org/cgi/content/full/318/5852/952/DC1Materials and MethodsFigs. S1 to S3Tables S1 and S2References and Notes

21 June 2007; accepted 4 October 200710.1126/science.1146842

Observation of the One-DimensionalDiffusion of Nanometer-SizedDislocation LoopsK. Arakawa,1* K. Ono,2 M. Isshiki,3 K. Mimura,3 M. Uchikoshi,3 H. Mori1

Dislocations are ubiquitous linear defects and are responsible for many of the properties ofcrystalline materials. Studies on the glide process of dislocations in bulk materials have mostlyfocused on the response of dislocations with macroscopic lengths to external loading or unloading.Using in situ transmission electron microscopy, we show that nanometer-sized loops with a Burgersvector of ½⟨111⟩ in a-Fe can undergo one-dimensional diffusion even in the absence of stressesthat are effective in driving the loops. The loop size dependence of the loop diffusivity obtained isexplained by the stochastic thermal fluctuation in the numbers of double kinks.

The hardness and toughness of crystallinematerials is often governed by the gener-ation and motion of linear defects termed

dislocations (1). Previous studies on the glideprocess of dislocations in bulk materials havefocused on the response of dislocations withmacroscopic lengths to external loading orunloading (1, 2). On the other hand, it is knownthat nanoscale dislocations can be formed as

loops in bulk materials by the agglomeration ofself-interstitial atoms, which are produced uponenergetic particle irradiation, in the shape ofdisks. Recent molecular dynamics (MD) calcu-lations have shown that in metals and alloys,extremely small interstitial-type dislocation loopswith diameters of less than a few nanometers canundergo fast one-dimensional (1D) glide diffu-sion in the direction of their Burgers vector, b,

even under zero stress (3–7). This phenomenonhas also been examined theoretically (8–10).Other computational and theoretical studieshave shown that the loop diffusion plays a cen-tral role in the degradation processes of mate-rials for nuclear fission and nuclear fusion, uponhigh-energy particle irradiation (11, 12).

One MD study has shown that the highlydiffusive loops with b values of ½[111] in a-Fe,which are smaller than ~2.4 nm in diameter,can be regarded as bundles of crowdions with[111] axes (6). A crowdion is a kind of a self-interstitial atom (13); it has a long-rangecompression-strain field in a close-packed direc-tion, and its center of mass can easily move one-dimensionally along the axis. The crowdionbundles move by the almost independent mo-tions of the constituent crowdions along their

Fig. 4. Schematic diagram of plausi-ble magmatic and hydrothermal pro-cesses responsible for 2004–2006accelerated Yellowstone caldera upliftand Norris subsidence. Black dots areearthquake hypocenters from October2004 to March 2007 (see Fig. 1A forthe epicenters). The yellow area showsthe seismically imaged magma bodyin Fig. 3E. Background colors repre-sent cubical dilatation, in unit changesof volume, induced by the modeledinflating sill. Fluids exsolved frommagma crystallization can be trappedbeneath the nonpermeable rocks nearthe brittle-ductile transition zone,taken as the 80th percentile focaldepth of earthquakes (white dashedline) (21, 22), to produce the calderauplift.

1Research Center for Ultra-High Voltage Electron Micros-copy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka567-0047, Japan. 2Department of Material Science,Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan. 3Institute of Multidisciplinary Research forAdvanced Materials, Tohoku University, 2-2-1 Katahira,Aoba-ku, Sendai 980-8577, Japan.

*To whom correspondence should be addressed. E-mail:arakawak@uhvem.osaka-u.ac.jp

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